HABERLAND, Hartmut. Sperantapük e Linglänapük as volapüks. Sprogforum. Tidsskrift for sprog- og kulturpædagogik, [S. l.], v. 12, n. 36, p. 28–34, 2006. DOI: 10.7146/spr.v12i36.114632. Disponível em: https://tidsskrift.dk/spr/article/view/114632. Acesso em: 5 dec. 2025.